Method of manufacturing semiconductor device having conductive thin films

ABSTRACT

In forming an electrode  2  on a silicon oxide film  5  on a semiconductor substrate  4  through a silicon oxide film  5,  for example, the gate electrode  2  is structured in a laminated structure of a plurality of polycrystalline silicon layers  6 . The portion of the gate electrode  2  is formed by a method of manufacturing a thin film having a process of depositing amorphous layers and a process of crystallizing (recrystallizing) this amorphous material. In this case, depositing of the amorphous layers is carried out dividedly by a plurality of times so that the thickness of an amorphous layer to be deposited at one time is not larger than a thickness to be prescribed by a critical stress value determined according to a fail event, the amorphous material is crystallized after each process of depositing each amorphous layer has been finished, and the process of depositing amorphous layers and the process of crystallizing the amorphous material are repeated, whereby a laminated structure of the polycrystalline layer 6 having a necessary film thickness is obtained. With the above-described arrangement, it is possible to prevent a deterioration of electric characteristics of a semiconductor device and an occurrence of a defect, such as a peeling off between layers, cracks in a layer, etc., and it is possible to obtain a polycrystalline layer of small grain size in a desired film thickness by a lamination of polycrystalline materials.

This application is a Divisional application of application Ser. No.10/265,105, filed Oct. 7, 2002, which is a Continuation application ofSer. No. 09/536,642, filed Mar. 28, 2000, which is a Continuationapplication of Ser. No. 08/985,179, filed Dec. 4, 1997, which is aDivisional application of Ser. No. 08/749,324, filed Nov. 14, 1996,which is a Divisional application of application Ser. No. 08/534,118,filed Sep. 26, 1995, which is a Divisional application of applicationSer. No. 08/432,065, filed May 1, 1995, which is a Divisionalapplication of application Ser. No. 08/168,506, filed Dec. 22, 1993, thecontents of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and amanufacturing method therefor, and relates more particularly to asemiconductor device that has a thin-film structure with a lamination ofpolycrystalline layers divided into layers, each having a thickness notlarger than a predetermined thickness prescribed according to a failevent, or a semiconductor device that has a thin-film structure with alamination of polycrystalline layers and layers of another material, ofwhich a main component thereof is different from the main component ofthe polycrystalline layers, for separating these polycrystalline layersfrom each other, a method of manufacturing this device, a manufacturingdevice therefor, and a method of determining a film thickness of thepolycrystalline layers for preventing a fail event of the semiconductordevice.

In recent years, amorphous materials have been used widely for variousapplications, such as for semiconductor device materials and magneticmaterials, by taking advantage of such characteristics as isotropy anduniformity that can be obtained from the amorphous materials. As amaterial for a semiconductor device, amorphous silicon has been widelyused for the purpose of easily obtaining a uniform density of animpurity.

When a silicon thin film has been formed as a polycrystalline silic onlayer on the surface of a semiconductor substrate, stress generatedwithin the film is sufficiently low so as to be not higher than a fewhundred MPa.

After an amorphous film layer has been formed on the surface of thesemiconductor substrate, when the amorphous film is exposed to a hightemperature higher than the temperature at which a previously-coatedamorphous material is crystallized for forming another film made ofother material on the film, or for carrying out a heat processing torelax a stress caused by the other layer, or for crystallizing theamorphous material of the film formed, the volume of the film shrinks asthe crystallization of the amorphous material progresses, with a resultthat, in some cases, an extremely large tensile stress reaching 1000 MPais generated within the film.

Because of failures (such as warp deformation in the wafer, peeling-offbetween layers, cracks within a layer, etc.) generated within thesemiconductor device due to the occurrence of this tensile stress, therehas been a case that the reliability of the product was deterioratedseriously. In order to prevent an occurrence of such a defect asdescribed above, a method has been taken that a film having acompressive stress generated within the film or a film having a tensilestress generated within the film is laminated to reduce the totalstress, for example as described in the Japanese Patent UnexaminedPublication No. JP-A-63-260052

In relation to the formation of a laminated layer of polycrystallinesilicon films in the semiconductor device, there are also othertechniques such as described in the Japanese Patent UnexaminedPublication No. JP-A-63-29954 and the Japanese Patent UnexaminedPublication No. JP-A-3-3326. These techniques provide the techniques forlaminating materials of mutually different substances.

However, when an amorphous film is formed on the surface of, thesemiconductor substrate and the film layer is crystallized to have apolycrystalline layer, the newly grown grain becomes larger as the filmthickness is larger and there is a tendency that the proportion of thevolume contraction becomes larger. As a result, de pending on thethickness of the film formed, the tensile stress generated in theamorphous material layer that has been crystallized becomes larger thanthe bonding strength between the film layers formed or the strength ofthe materials of the film layers formed, which may result in a failuresuch as a peeling off between layers or a crack within a layer.

Further, even if the above-described failure has not occurred in thesemiconductor device, a film thickness has become a cause for generatinga warp deformation in the wafer which may cause a fault at the time ofan exposure, or an increase in the dislocation density following anincrease in the strain at a film interface of the amorphous material hascaused a deterioration in the electric characteristics within thesemiconductor device such as an increase in the electric conductivity oran inter-connection. Thus, it has been necessary to provide a limit to afilm thickness at the time of forming films in order to control a stresswithin a film.

In the specification of the present invention, various defects inducedby an increase in the stress generated within the semiconductor devicewill collectively be referred to as “a fail event of the-semiconductordevice”. An allowable stress level at which none of these fail eventswill occur may change widely depending on a difference in the process ofmanufacturing a semiconductor device, a difference in portions of alaminated film which are used for a semiconductor device, physicalproperties of materials used and a corresponding fail event. Therefore,an allowable stress value at which a fail event of the semiconductordevice will not occur will be called a critical stress value”.

When a thickness of a polycrystalline phase film which has been obtainedby crystallizing an amorphous phase film is small, the crystal grainsbecome fine and a stress generated is lowered and no defect, describedin the foregoing will occur. However, the thin film thickness haslimited an allowable current that can flow within the film and also hasbecome a cause for a defect such as an electromigration that isgenerated by an excess current within the film. Thus, it has beendifficult to form a film with an optimum film thickness by using apolycrystalline phase film which was produced by crystallizing anamorphous material layer.

SUMMARY OF THE INVENTION

Objects of the Present Invention are as Follows.

(1) In a thin-film manufacturing method having a process of depositingamorphous layers and a process of crystallizing the amorphous materials,it is an object of the present invention to provide a method ofmanufacturing a semiconductor device which can form a film thickness ofa required design specification for a thin film structure made of theconductive material that includes an amorphous layer to be crystallizedin a later process, and which can eliminate defects, such as adeterioration of electric characteristics of the semiconductor devicemanufactured, peeling-off between layers, cracks within a layer, etc.

(2) It is an object of the present invention to provide a semiconductordevice of a high reliability which can prevent an occurrence of a defectby the method of manufacturing a semiconductor device that is providedin (1).

(3) In a thin-film manufacturing device which can carry out a process ofdepositing amorphous layers and a process of crystallizing the amorphousmaterials, it is an object of the present invention to provide a devicefor manufacturing a thin film which can automatically control theprocess of forming an amorphous layer and the process of crystallizingthe amorphous material, in an integrated process without exposing thethin film in manufacturing to the atmosphere.

(4) In order to achieve the objects (1) to (3) of the present invention,it is an object of the present invention to provide a method of-determining a maximum value of a film thickness in which an amorphouslayer can be deposited at one time to ensure that an occurrence of afail event is prevented, not based on experience.

In order to achieve the above-described objects, the present inventionhas the following characteristics.

A semiconductor device of the present invention has conductive thinfilms and is characterized by the following. (1) At least a part of thethin-film has a laminated structure divided along a film thicknessdirection, and each of the divided layers has a main component made ofthe same element or the same compound. (It is desirable that the maincomponent is a material including silicon atom or metal silicide. Thematerial of each layer may be different from that of the other bydoping). (2) At least a part of the thin-film has a laminated structuredivided along a film thickness direction, and an average crystal grainsize of the grains within each one of the divided layers is about ½times to about ten times of the thickness of the divided layer. (Forexample, the grain size is equal to the thickness of the divided film oris in the same order or is about a fraction or several times as thedivided film thickness.) (3) Additionally, or alternately, at least apart of the thin-film has a laminated structure divided along a filmthickness direction, and the thickness of each layer is not larger thana thickness prescribed by a critical stress value that is determinedaccording to a fail event of the semiconductor device.

In either case, a semiconductor device is the one having a thin-filmstructure made of the same conductive material and it is desirable thatthe thin film is divided, at least once, along its film thicknessdirection. It is also desirable that the thin film consists of at leasttwo polycrystalline layers and the thin film is applied to a portionselected from a group of electrodes (preferably a gate electrode) andwiring layers. It is also effective to have another layer made of amaterial different from that of the polycrystalline layer, at a positionfor separating the polycrystalline layer into layers. It is alsoeffective to have different densities of impurity in adjacent layers ofat least one pair of adjacent layers of the thin film divided along thefilm thickness direction.

The semiconductor device of the present invention is also characterizedin that a trench or a rugged surface is provided on the surface of thesemiconductor substrate, that a conductive multi-layer thin film isformed on a part or a whole of the trench or the rugged surface of thesurface of the semiconductor substrate so as to cover a portion of acorner formed by at least the semiconductor substrate surface, thetrench and the rugged surface, and that each layer has a main componentwhich is the same element or the same compound. In this case, it isdesirable that the conductive multilayer thin film is polycrystallineand the thickness of each layer structuring the thin film is not largerthan the thickness prescribed by a critical stress level to bedetermined according to a fail event of the semiconductor device. It isalso effective to have a layer made of a material different from that ofthe polycrystalline layers, at a position for separating adjacent onesof the polycrystalline layers. It is also effective to have differentdensities of impurity at least between a pair of adjacent layers of thethin film divided in the film thickness direction.

The semiconductor device of the present invention is also characterizedin that it has a laminated layer structure of a metal silicide thin filmdivided along a film thickness direction by at least one time.

Implementation status of the semiconductor device according to thepresent invention is as follows. (1) The semiconductor has apolycrystalline layer obtained from the process of depositing anamorphous layer and a process of crystallizing the amorphous materialand there are at least two continuous deposited layers ofpolycrystalline material whose main component is made of the samematerial. (2) Each of the laminated polycrystalline layers has athickness not larger than a thickness prescribed by a critical stresslevel determined according to a fail event of the semiconductor device.(3) In a semiconductor device having a gate electrode, there are atleast two continuous deposited layers of polycrystalline material whosemain component is the same material in the whole or part of the gateelectrode structure on the semiconductor substrate.

The method of manufacturing a semiconductor device according to thepresent invention includes a process of depositing layers of amorphousmaterials on the semiconductor substrate and a process of crystallizingthe deposited amorphous materials, and is characterized in that either(1) the process of depositing layers of amorphous materials is dividedinto a plurality of times and the crystallization is carried out foreach process of depositing each amorphous layer, or (2) the process ofdepositing amorphous layers is divided into a plurality of times, amaterial whose main component is different from that of the amorphousmaterial, is deposited to separate an amorphous layer from an adjacentamorphous layer at each process of depositing each amorphous layer andthe amorphous material is crystallized at least after finishing all thedeposition processes. In the case of (2), it is desirable that theamorphous material is silicon and the main component for separating theamorphous layers which is different from the amorphous material is ametal which generates a silicide reaction.

In either case, it is desirable that the method of manufacturing asemiconductor device according to the present invention includes theprocess of differentiating, between at least a pair of adjacent layers,the density of impurity therein, or includes the process ofcrystallizing the amorphous material which is the crystallizationprocess of an amorphous material by a laser irradiation on either thewhole surface of the amorphous layer or on only a selective localportion of the amorphous layer.

The deposition method of thin films according to the present inventionincludes a process of depositing layers of amorphous materials and aprocess of crystallizing the amorphous materials, and is characterizedin one of the following: (1) the process of depositing layers ofamorphous materials is divided into a plurality of times and thecrystallization process is applied to each amorphous layer, (2)densities of impurity within the plurality of layers of amorphousmaterials are different between at least an adjacent pair of layers, (3)the process of depositing amorphous layers is divided into a pluralityof times, a material whose main component is different from that of theamorphous material is deposited to separate an amorphous layer from anadjacent amorphous layer and the amorphous layers are crystallized atleast after finishing all the processes, and (4) the process ofcrystallizing the amorphous material which is the crystallizationprocess of an amorphous material by a laser irradiation on either thewhole surface of the amorphous layer or on only a selective localportion of the amorphous layer.

The method of manufacturing a thin film according to the presentinvention is a method of obtaining a metal silicide thin film bygenerating a silicide reaction by laminating a silicon thin film with ametal thin film, and is characterized in that a metal thin film and asilicon thin film are laminated at least two times respectively and thatthe film thickness of each laminated layer is not thicker than a filmthickness prescribed by a fail event and the metal silicide thin film ismanufactured by generating a silicide reaction.

In either case, it is desirable that the method of manufacturing a thinfilm according to the present invention provides a film thickness ofeach amorphous layer deposited at one time to be not larger than a filmthickness prescribed by a critical stress value that is determinedaccording to a fail event.

The device for manufacturing a semiconductor device according to thepresent invention is a device for carrying out a process of depositinglayers of amorphous materials and a process of crystallizing theamorphous material and is characterized in that the manufacturing devicehas a chamber for installing a semiconductor substrate in it, a tool forsupporting the semiconductor substrate, a heating unit for adjusting atemperature inside the chamber and a temperature of the substrate, unitsfor adjusting volumes of gases to be taken in corresponding to thenumber and kinds of gas to be flown into the chamber, a unit foradjusting a pressure of gas inside the chamber, an exhaust unit forexhausting air from the chamber, and a unit for automaticallycontrolling said chamber, said heating unit, said flow rate adjustingunit, said gas pressure adjusting unit and said exhausting unit, and thecontrol unit controls a process of continuously or intermittentlydepositing amorphous thin films a plurality of times and a process ofcrystallizing these thin films, to form a laminated thin film structureon the semiconductor substrate. It is desirable that this device has atleast one laser irradiating unit and a unit for automaticallycontrolling this laser irradiating unit to carry out an automaticcontrol and an automatic processing in the processes of manufacturing asemiconductor device.

The method of determining a film thickness according to the presentinvention is a method of determining a film thickness of deposited thinfilms for carrying out a process of depositing layers of amorphousmaterials and a process of crystallizing the amorphous material, and ischaracterized in that a film thickness of an amorphous layer to bedeposited at one time is determined to be a level not higher than acritical stress value to be determined according to a fail event, basedon a relationship between a film thickness of an amorphous layer and anaverage size of a crystal grain generated in a polycrystalline layerobtained by crystallizing the amorphous material and a relationshipbetween a film thickness of a polycrystalline layer obtained bycrystallizing the amorphous material and a stress generated.

Terms to be used in the specification of the present invention will beexplained as follows.

Main component: This refers to a portion excluding three types ofimpurities; an impurity for positively carrying out doping, an impurityoriginally included in a raw material such as a gas or a target, and animpurity which is unavoidably mixed into a semiconductor during amanufacturing process.

Conductivity (of a thin film): This refers to a conductivity of a metalor semiconductor. In other words, volume resistivity of a semiconductoris between a metal and an insulator and is about 10⁻⁵ to 10⁸ Ω·m. Thevolume resistivity is lower as the impurity density is higher, and thisshows a value near 0 at an absolute zero degree. Accordingly, whenvolume resistivity of a thin film is not higher than 10⁸ Ω·m, the thinfilm is said to have a conductivity according to the present invention.

Average grain size of crystal (in a deposited film surface): A densityof an occurrence of a crystal nucleus differs depending on an impuritydensity of a deposited film and a heating condition, and this becomes ½times to 10 times depending on a condition for an occurrence of acrystallization. In the present invention, a crystallization (reaction)of a grain size of about ½ times to 10 times of a film thickness of eachdivided layer is desirable.

A layer generated by a silicide reaction: A layer may be amorphous orpolycrystalline at time of deposition and a film to be formed in the endshould be polycrystalline.

A fail event of a semiconductor device: A collective name of variousfailures caused by an increase in the stress generated within asemiconductor device, such as a peeling-off between layers, a crackwithin a layer, or a crystalline defect.

Allowable stress level: An allowable stress value at which a fail eventof a semiconductor will not occur. A permissible stress level at which afail event will not occur varies depending on a difference in a processof manufacturing a semiconductor device, a difference in a portion atwhich a laminated film is used for a semiconductor device, physicalcharacteristics of a material a-corresponding fail event, etc.

Trench capacitor: a capacitor to be used for a memory cell of a DRAM(Dynamic Random Access Memory) whose memory capacity exceeds 1 M bits.When a capacitor is provided in a side wall of a deep trench formed byetching a silicon substrate to increase capacitance, a large capacitancecan be obtained even if a capacitor area becomes finer further.

LOCOS: A silicon oxide film for electrically separating among devices.

Primary recrystallization: If a range in which an atom is arrayedorderly is considered to be a crystal, it can be considered from a microviewpoint that a crystal also exists within a substance of an amorphousstate. However, primary recrystallization in the present inventionrefers to a phase change of an amorphous substance into a crystal, thatis, a crystallization (reaction). Generally, a primary recrystallizationrefers to a fining of crystal grains when a material which has been coldworked and composed of many crystal defects has been heated. However, inthe present invention, this term is used to emphasize that an averagesize of a grain is approximately a size obtained by a primaryrecrystallization, which is discriminated from a secondaryrecrystallization where a fine crystal grows large at a temperature anatom is activated.

It has been generally known that when the process of crystallizing anamorphous material is carried out at a temperature at which a primaryrecrystallization reaction is generated after the process of depositingfilms of amorphous layers, the size of a crystal grain of a filmobtained by crystallizing the amorphous material becomes an order of afilm thickness and a film with almost no existence of a grain boundaryin the film thickness direction is formed.

The grain boundary is an incommensurate portion between crystal grainsat which atomic array directions do not agree with each other and,therefore, a region where many local defects (such as a dislocation, alattice vacancy, and a cavity) exist.

In crystallizing an amorphous material by heat processing, when a filmthickness is large, the crystal grain size becomes large and the ratioof a grain boundary which holds a higher defect density in the totalfilm region is small, so that the ratio of a volume contraction of thefilm becomes large and a tensile stress within the film becomes large.On the other hand, when the film thickness is small, the crystal grainsize becomes small, and a ratio of a grain boundary in the total filmregion becomes relatively large. Therefore, the ratio of a volumecontraction becomes relatively small and a tensile stress can beminimized.

The crystal grain size referred to in this specification means anaverage value of a distance between adjacent grain boundaries in adirection on parallel to the film surface in a desired cross section ofa polycrystalline thin film in which a crystallization reaction has beencompleted.

FIG. 15 shows an example of a measurement of a stress (crystallizationstress) generated as a result of a crystallization reaction carried outwithin an amorphous silicon film by changing a film thickness. In FIG.15, the horizontal axis shows a total thickness of films deposited andthe vertical axis shows a stress generated inside the films as a resultof a crystallization reaction when the total films deposited have beencrystallized at one time. As shown by this drawing, it is clear thatwhen the thickness of films deposited increases the stress generated atthe time of the crystallization reaction increases.

Accordingly, it is effective to control the film thickness so that thestress generated by the crystallization reaction is set to be not higherthan a critical stress level prescribed by each fail event, to preventan occurrence of a peeling between thin films, cracks within thin filmsor a dislocation inside the semiconductor substrate.

According to the present invention, in the process of manufacturing asemiconductor device including the process of depositing amorphouslayers, the thickness of amorphous layers deposited at one time islimited to be not higher than a thickness prescribed by a criticalstress level determined according to a fail event and the amorphousmaterial is crystallized, so that the size of a crystal formed within apolycrystalline layer obtained by the primary recrystallization of theamorphous layers is limited to be on the order of a thickness of filmsof the amorphous layers deposited.

As a result, the size of the crystal grains formed within apolycrystalline layer is limited and the stress generated within thepolycrystalline layer can be reduced to be not higher than the criticalstress level at which a fail event is not generated.

By laminating the polycrystalline layers whose stress has been reduced,the film thickness of the thin film structure can be set to thethickness necessary for the specification of a design, and it ispossible to prevent an occurrence of a deterioration of electriccharacteristics of a semiconductor device to be manufactured and defectssuch as peeling-off between layers and cracks within a layer induced bya stress. Thus, it is possible to obtain a high reliability of asemiconductor device to be manufactured and a high production yield ofthe product.

Further, in the thin film manufacturing device which can carry out theprocess of depositing amorphous layers and the process of crystallizingthe amorphous material, it is possible to carry out the process ofdepositing films of amorphous layers and the process of crystallizingthe amorphous material by an automatic control in an integrated processwithout exposing the thin films during a manufacturing process into theatmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view for showing a schematic cross section of asemiconductor device in one embodiment of the present invention.

FIG. 2 is a schematic cross sectional view for showing a firstmanufacturing process of a semiconductor device according to the presentembodiment.

FIG. 3 is a schematic cross sectional view for showing a secondmanufacturing process of a semiconductor device according to the presentembodiment.

FIG. 4 is a schematic cross sectional view for showing a thirdmanufacturing process of a semiconductor device according to the presentembodiment.

FIG. 5 is a schematic cross sectional view for showing a fourthmanufacturing process of a semiconductor device according to the presentembodiment.

FIG. 6 is a schematic cross sectional view for showing a fifthmanufacturing process of a semiconductor device according to the presentembodiment.

FIG. 7 is a schematic cross sectional view for showing a sixthmanufacturing process of a semiconductor device according to the presentembodiment.

FIG. 8 is a schematic cross sectional view for showing a seventhmanufacturing process of a semiconductor device according to the presentembodiment.

FIG. 9 is a schematic cross sectional view for showing an eighthmanufacturing process of a semiconductor device according to the presentembodiment.

FIG. 10 is a schematic cross sectional view for showing a ninthmanufacturing process of a semiconductor device according to the presentembodiment.

FIG. 11 is a schematic cross sectional view for showing a tenthmanufacturing process of a semiconductor device according to the presentembodiment.

FIG. 12 is a schematic cross sectional view for showing an eleventhmanufacturing process of a semiconductor device according to the presentembodiment.

FIG. 13 is a schematic cross sectional view for showing a twelfthmanufacturing process of a semiconductor device according to the presentembodiment.

FIG. 14 is a schematic cross sectional view for showing a manufacturingprocess of conductive thin films of a semiconductor device according tothe present embodiment.

FIG. 15 is a graph for showing a relationship between thickness of filmsand a crystallization reaction in amorphous silicon thin films forexplaining the operation of the present invention.

FIG. 16 is a perspective view for showing a schematic cross section of asemiconductor device in another embodiment of the present invention.

FIG. 17 is a schematic cross sectional view for showing a manufacturingprocess of conductive thin films of a semiconductor device according tothe present embodiment.

FIG. 18 is a schematic cross sectional view for showing a manufacturingprocess of a laminated layer structure of conductive thin films of asemiconductor device according to the present invention.

FIG. 19 is a schematic cross sectional view for showing a manufacturingprocess of a laminated layer structure of conductive thin films of asemiconductor device according to the present invention.

FIG. 20 is a schematic cross sectional view for showing a manufacturingprocess of a laminated layer structure of conductive thin films of asemiconductor device according to the present invention.

FIG. 21 is a schematic cross sectional view for showing a manufacturingprocess of a laminated layer structure of conductive thin films of asemiconductor device according to the present invention.

FIG. 22 is a schematic cross sectional view for showing a manufacturingprocess of a laminated layer structure of conductive thin films of asemiconductor device according to the present invention.

FIG. 23 is a schematic cross sectional view for showing a manufacturingprocess of a laminated layer structure of conductive thin films of asemiconductor device according to the present invention.

FIG. 24 is a schematic cross sectional view for showing a manufacturingprocess of a laminated layer structure of conductive thin films of asemiconductor device according to the present invention.

FIG. 25 is a schematic cross sectional view for showing a manufacturingprocess of a laminated layer structure of conductive thin films of asemiconductor device according to the present invention.

FIG. 26 is a schematic cross sectional view for showing a manufacturingprocess of a laminated layer structure of conductive thin filmsutilizing a metal silicide layer of a semiconductor device according tothe present invention.

FIG. 27 is a microscopic photograph for showing a cross section of alaminated structure shown in FIG. 26.

FIG. 28 is a schematic cross sectional view for showing a manufacturingprocess of a laminated layer structure of conductive thin filmsutilizing a metal silicide layer of a semiconductor device according tothe present invention.

FIG. 29 is a schematic cross sectional view for showing a manufacturingprocess of a laminated layer structure of conductive thin filmsutilizing a metal-silicide layer of a semiconductor device according tothe present invention.

FIG. 30 is a drawing for showing a schematic structure of amanufacturing device for manufacturing a semiconductor device accordingto the present invention.

FIG. 31 is a drawing for showing a schematic structure of amanufacturing device for manufacturing a semiconductor device in anotherembodiment according to the present invention.

FIG. 32 is a flow chart for controlling the manufacturing devices shownin FIGS. 30 and 31.

FIG. 33 is a drawing for explaining one example of controlling atemperature of a semiconductor substrate in the process of manufacturinga semiconductor device.

FIG. 34 is a flow chart for controlling the manufacturing devices shownin FIGS. 30 and 31.

FIG. 35 is a drawing for showing a schematic configuration of amanufacturing device utilizing a sputtering method for manufacturing asemiconductor device in another embodiment according to the presentinvention.

FIG. 36 is a graph for showing one example of controlling a temperatureof a semiconductor substrate and a speed of depositing thin films in theprocess of manufacturing a semiconductor device shown in FIG. 35.

FIG. 37 is a drawing for showing another embodiment for manufacturing alaminated thin film structure of a semiconductor device according to thepresent invention.

FIG. 38 is a graph for showing one example of controlling a density ofan impurity in each laminated film in the manufacturing process shown inFIG. 37.

FIG. 39 is a drawing for showing another embodiment for manufacturing alaminated thin film structure of a semiconductor device according to thepresent invention.

FIG. 40 is a drawing for showing an embodiment for manufacturing awiring film by a laminated thin film structure of a semiconductor deviceaccording to the present invention.

FIG. 41 is a flow chart for showing a method of determining a filmthickness of each laminated thin film structure according to the presentinvention.

FIG. 42 is a graph for showing a relationship between a crystal grainsize and a stress generated, to be utilized in the method of determininga film thickness according to the present invention.

FIG. 43 is a graph for showing a relationship between a film thicknessand a stress generated, to be utilized in the method of determining afilm thickness according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be explained below withreference to the drawings.

A first embodiment of the present invention relating to a semiconductordevice and a method of manufacturing the semiconductor device based onthe present invention will be explained with reference to FIGS. 1 to 14.

FIG. 1 is a cross sectional perspective view for showing a configurationof a semiconductor device 1 based on the embodiment of the presentinvention. The semiconductor device 1 shows a state that the processesof a LOCOS formation, a gate oxidization, a deposition of a gateelectrode film and an etching have been completed, and the presentinvention is utilized as a gate electrode structure of an MOStransistor.

According to the present embodiment, on the surface of the p-typesilicon semiconductor substrate 4 which is electrically insulated fromthe adjacent element by the LOCOS 3, a gate electrode 2 is structured bya silicon oxide film 5 formed by a heat oxidization process, and dividedpolycrystalline silicon layers 6 in which an impurity, such as P(phosphorus), for electrically activating silicon has been doped in highdensity and uniformly are laminated on the surface of the silicon oxidefilm 5. Each of the divided polycrystalline silicon layers 6 is inmainly columnar structure by a primary recrystallization.

The method of manufacturing the semiconductor device 1 will be explainedby taking an example of manufacturing a CMOS on the p-type siliconsemiconductor substrate 4 by referring to cross sectional views of themanufacturing process shown in FIGS. 2 to 14.

A first process is shown in FIG. 2. The surface of the p-type siliconsemiconductor substrate 4 is thermally oxidized to form a silicon oxidefilm 5 a. Next, a silicon nitride film 11 a is deposited on the surfaceof the silicon oxide film 5 a by CVD (chemical vapor deposition) or thelike.

A second process which continues the first process is shown in FIG. 3. Aphotoresist 12 a is coated uniformly on the surface of the siliconnitride film 11 a deposited in the process shown in FIG. 2, thephotoresist 12 a is patterned and the silicon nitride film 11 a isetched. By controlling the flow rate of phosphine (PH3), phosphorus (P)is ionized by an electric discharge and the phosphorus (P) is doped to aportion on the semiconductor substrate where the nitride silicon film 11a has been lost by the etching, with the remained silicon nitride film11 a used as a mask. Although a phosphorus (P) ion has been implanted byusing phosphine, instead of this ion, an arsenic (As) ion may also beimplanted by using arsine (AsH₃) or the like. The above ion implantationis carried out to complete an insulation between devices by using theLOCOS portion as an inverse bias.

After the second process, at a third process (FIG. 4), a thermaloxidation or the like is carried out to form a thick silicon oxide film5 a at only the area for preventing a next ion implanting.

FIG. 5 shows a fourth process. In this process, only the silicon nitridefilm 11 a in the process of FIG. 4 is selectively etched to remove thisportion. Next, a boron ion is generated by an electric discharge fromboron trifluoride (BF₃) to dope the boron ion to the p-type siliconsemiconductor substrate 4. The p-type silicon semiconductor substrate 4is amorphous in this state because of a damage due to the ionimplantation, or even if the p-type silicon semiconductor substrate 4 ismono-crystal it shows a very high volume resistivity because ofelectrical inactivity due to an existence of many lattice defects.Accordingly, by carrying out a thermal annealing, the impurity that hasbeen doped is diffused and the p-type silicon semiconductor substrate 4is recovered.

FIG. 6 shows a fifth process. A silicon nitride film 11 b is depositedby a CVD method or the like and a portion for forming a LOCOS 3 isetched to provide a mask. After removing a remaining photoresist 12 b,the LOCOS 3 is formed by a wet oxidation or the like.

Next, in a sixth process shown in FIG. 7, the silicon nitride film 11 bused for forming the LOCOS 3 is removed by using thermal phosphoric acidor the like and the silicon oxide film Sa except the LOCOS 3 is alsoremoved by etching. On the surface of the exposed p-type siliconsemiconductor substrate 4, a new thin silicon oxide film 5 is formed asa gate electrode oxide film by a thermal oxidation again.

After this process, a process of depositing a gate electrode material iscarried out. The method of manufacturing the gate electrode 2 bylaminating the divided polycrystalline silicon layers 6 in which animpurity for electrically activating silicon has been doped in a highdensity and a uniform density, shown in FIG. 1, will be explained withreference to FIG. 14.

FIG. 14 is a cross section of the process for manufacturing the gateelectrode 2, based on the present invention., shown in FIG. 1, for asemiconductor device having the divided polycrystalline silicon layers 6in which an impurity for electrically activating silicon has been dopedin a high density and a uniform density.

A process ST1 of FIG. 14 will be explained first. Temperature of asemiconductor substrate is controlled, for example, in order to depositamorphous silicon by vapor-phase reacting disilane Si₂H₆ and phoshinePH₃ gases. Then, divided amorphous silicon layer 13 is deposited on thesurface of the p-type silicon semiconductor substrate 4 on which thesilicon oxide film 5 was formed by the gate oxidation at the precedingprocess, by a CVD or the like, at a film thickness to be deposited atone time film formation not larger than a film thickness prescribed by acritical stress determined according to a fail event. In this case,density of the impurity phosphorus (P) within the divided amorphoussilicon layers 13 is uniform.

In the above example, temperature of the semiconductor is used as afactor for controlling the deposited phase of silicon, it is needless tomention that other factors, such as a pressure or a flow rate of a gas,for example, may also be controlled. In the case of depositing amorphoussilicon thin films, monosilane SiH₄ may also be used.

Processes ST2 to ST3 in FIG. 14 will be explained next. By holding thetemperature of the semiconductor substrate 4 at 600° C. or above, theamorphous silicon is crystallized and the divided polycrystallinesilicon layers are formed. The stress generated in the dividedpolycrystalline silicon layers 6 is restricted to be not higher than acritical stress level as the film thickness of the divided amorphoussilicon films 13 is limited to be not higher than the film thicknessprescribed by the critical stress level determined according to a failevent. The amorphous material may be crystallized by controlling thetemperature of the semiconductor substrate or may also be crystallizedby irradiating a laser. Crystallization of the amorphous material by alaser irradiation may be applied for the crystallization of the wholesurface of the divided amorphous silicon layers 6 deposited on thesemiconductor substrate 4 or for a local crystallization of the dividedamorphous silicon layers 6 by an irradiation at a local position.

At processes ST4 in FIG. 14, the processes ST1 to ST3 in FIG. 14 arerepeated until the total film thickness of the laminated dividedpolycrystalline silicon layers 6 has reached a required thickness. Byrepeating this process, divided polycrystalline silicon film 14 with alow stress is formed at process ST5 in FIG. 14.

After the process of FIG. 14, a photoresist 12 c (reference FIG. 7) iscoated on the surface of the divided polycrystalline silicon film 14 tocarry out a process of patterning, and the divided polycrystallinesilicon film 14- is etched, so that the gate electrodes 2 of thestructure having the laminated polycrystalline silicon layers 6 can befinally formed as shown in the process of FIG. 8.

Accordingly, by laminating the polycrystalline silicon layers 6 of whichan impurity for electrically activating, such as phosphorus (P), is ofhigh density and uniform density, a cross section area or a filmthickness which does not cause an excessive electric resistance can beobtained. As an average size of the crystal grain of the polycrystallinesilicon thus formed is small, it is possible to obtain the gateelectrode 2 having structure of the laminated divided polycrystallinesilicon layers 6, with stress generated within the film restricted to benot higher than the critical stress.

FIG. 27 shows a photograph, of an example of an observation by anelectron microscope, of a thin film having a structure of laminatedpolycrystalline layers which has been formed by depositing amorphoussilicon and crystalline cobalt layers alternately and then formingpolycrystalline layers with columnar structure by a primaryrecrystallization reaction. Its magnification is about 180 thousandtimes.

As shown in FIG. 27, the laminated structure of the dividedpolycrystalline silicon layers 6 can be also observed by an electronmicroscope and this structure is clearly different from a structureobtained by depositing a polycrystalline material layer having necessarythickness in that clear borders of divided layers can be recognized inthis picture.

An eighth-process which continues will be explained with reference toFIG. 9. A photoresist 12 d is coated on the p-type silicon semiconductorsubstrate to carry out a patterning. In this case, with-the remainingphotoresist 12 d used as mask, a phosphorus (P) or arsenic (As) ion isimplanted to form a source and a drain of an n-channel MOS transistor.

FIG. 10 shows a ninth process. At first, the photoresist used in theprocess of FIG. 9 is removed and a photoresist 12 e is coated on thep-type silicon semiconductor substrate 4 to carry out a patterning.Then, a boron (B) ion or the like is implanted to form a source and adrain of the p-channel MOS transistor. Thermal annealing is carried outto diffuse the doped ion.

At a following tenth process shown in FIG. 11, the photoresist 12 e usedat the process of FIG. 10 is removed and the p-type siliconsemiconductor substrate 4 is covered with an inter-layer insulation film16 such as phosphorus glass or the like. Holes 20 for obtaining anelectrical contact with the substrate are obtained by etching.

FIG. 12 (an 11th process) shows the processes of sputtering a wiringmaterial film such as an aluminum alloy film or the like on the surfaceof the p-type silicon semiconductor substrate 4 and patterning thisfilm, to obtain an aluminum alloy wiring layer 17. In FIG. 13 (a 12thprocess), in order to passivate the formed semiconductor device, thewhole surface of the substrate is covered by an insulation film (apassivation film) 18 thus ending the whole process. In the case of thesemiconductor device having a multi-layer wiring, a hole for obtaining afurther electrical contact is etched after the 12th process and then thenext wiring is sputtered. A wiring to a gate electrode is sputtered by aknown technique not shown.

Although in the first embodiment, a p-type silicon semiconductorsubstrate 4 has been used as a semiconductor substrate, it is needlessto mention that this should not necessarily be the p-type but an n-typesilicon semiconductor substrate may also be used. In this case, somemodification to the manufacturing process is necessary. A galliumarsenic semiconductor substrate or others may also be used instead.Although polycrystalline silicon has been used as the material for thegate electrode 2, other conductive material can also be used when it canbe deposited in an amorphous phase and when it is crystallized. AlthoughP (phosphorus) has been used as an impurity, another impurity such as B(boron), As (arsenic), etc. may also be used instead.

Another embodiment relating to a semiconductor device and a method ofmanufacturing the semiconductor device according to the presentinvention will be explained with reference to FIGS. 16 and 17.

FIG. 16 is a cross section perspective view for showing a structure ofthe semiconductor device 7 according to the other embodiment of thepresent invention. A semiconductor device 7 shows a state that a LOCOSdeposition, a gate oxidation, a film formation for the gate electrodeand an etching process have been completed. The method of manufacturinga semiconductor device based on the present invention is utilized forproviding a gate electrode structure of the MOS transistor in the samemanner as in the first embodiment.

A gate electrode 8 according to one embodiment of the manufacturingmethod is formed on the surface of a silicon oxide film 5 formed by athermal oxidation on the surface of a p-type silicon semiconductorsubstrate 4 which is electrically insulated from an adjacent device by aLOCOS 3. Divided polycrystalline silicon layers 6 into which an impuritysuch as P (phosphorus) or the like for electrically activating siliconhas been doped in a high density and a uniform density and a materialsuch as an aluminum alloy layer 9 which is different frompolycrystalline silicon including only silicon as a main component arelaminated alternately.

Except the gate electrode 8, this semiconductor device 7 can be obtainedby a manufacturing method similar to the manufacturing method of thesemiconductor device 1 shown in the first embodiment. Therefore, onlythe method of manufacturing the gate electrode 8 will be explained withreference to the process in FIG. 7 and FIG. 17.

A method of manufacturing the semiconductor device 7 is the same as thatof the first embodiment up to the middle of the process of FIG. 7. Afterending the process of FIG. 6, a silicon nitride film 11 b used forforming the LOCOS 3 in the process of FIG. 7 is eliminated by using hotphosphoric acid, and a silicon oxide film 5 a other than LOCOS 3 iseliminated by an etching. On the exposed surface of the p-type siliconsemiconductor substrate, a new thin silicon oxide film 5 is formed as anoxide film for the gate electrode by a thermal oxidation again.

After this process, a process for forming a film by using a gateelectrode material is carried out. Next, by referring to FIG. 17,description will be made of a method of manufacturing the gate electrode8 having a structure that a laminated thin film of dividedpolycrystalline silicon layers 6 into which an impurity (such as P, forexample) for electrically activating silicon has been doped in a highdensity and a uniform density are separated from each other by aluminumalloy layers 9 which are made of a material different from thepolycrystalline silicon which uses only silicon as a main component.

FIG. 17 is a cross section of the process for showing the method ofmanufacturing the gate electrode 8 of the semiconductor device 7according to the second embodiment of the present invention.

A process ST1 of FIG. 17 will be explained below. After forming thesilicon oxide film 5 for the gate electrode, a gas including an impurityto be doped such as disilane (Si₂H₆) and phosphine (PH₃), for example,is flown on the surface of the silicon oxide film 5 to carry out a vaporphase reaction. Then, a divided amorphous silicon layer 13 in a filmthickness not larger than a thickness prescribed by a critical stress tobe determined according to a fail event is deposited by a CVD (chemicalvapor deposition) or the like. Monosilane SiH₄ may also be used for adeposition of amorphous silicon thin films.

A process ST2 of FIG. 17 will be explained next. A material differentfrom the film deposited in the process ST1, such as aluminum alloylayers 9, is deposited by sputtering or the like. The material to bedeposited by sputtering may also be other conductive material such assilicide compound. A film thickness of the aluminum alloy layers 9 to bedeposited is the thickness at which an atom within each dividedamorphous silicon layer may scarcely move to other divided amorphoussilicon layer by a thermal diffusion in the subsequent process ofcrystallizing the divided amorphous silicon layers.

In a process ST3 of FIG. 17, the processes ST1 to ST2 are repeated untilthe total laminated layer thickness of the divided amorphous siliconlayers 13 and the polycrystalline aluminum alloy layers 9 becomes largerthan a necessary thickness.

A process ST4 of FIG. 17 will be explained next. When the totallaminated layer thickness of the divided amorphous silicon layers 13 andthe polycrystalline aluminum alloy layers 9 has reached the necessarythickness, the temperature of the semiconductor substrate is controlledto at least a temperature at which the amorphous silicon iscrystallized, for example 600° C. or above, to crystallize the wholedivided amorphous silicon layers 13.

After this manufacturing process of FIG. 17, the laminated thin film ofthe divided amorphous silicon layer 13 and the polycrystalline aluminumalloy layers 9 is patterned, to obtain the gate electrode 8 which hasthe structure that a laminated thin film of divided polycrystallinesilicon layers 6 into which an impurity such as P (phosphorus) forexample for electrically activating silicon has been doped in a highdensity and a uniform density is stacked with aluminum alloy layer 9which are made of a material different from the polycrystalline siliconwhich uses only silicon as a main component. A symbol 15 designates athin film having a structure of alternate laminated layers ofpolycrystalline silicon and the other material.

This manufacturing process does not require a crystallization process ofan amorphous material after each process of depositing an amorphous filmas in the first embodiment. With only one crystallization process afterending the whole film depositing process, the structure of the electrode8 based on this embodiment of the present invention can be obtained,which leads to a reduction in the number of processes.

For the material which is different from amorphous silicon to bedeposited in the process ST2 of FIG. 17, a metal which carries outsilicide reaction such as tungsten or cobalt can be used instead of analuminum alloy. Silicide reaction is progressed at an interface betweeneach divided amorphous silicon layer 13 and each silicide reacting metallayer so that a thin film of the structure having a lamination ofsilicide layers can be formed.

Thus, by setting the film thickness of each divided silicide layerobtained in this case to be not larger than the film thicknessprescribed by a critical stress level to be determined according to afail event, the stress generated within each divided polycrystallinesilicide layer can be minimized to be within the critical stress level.

As explained above, by providing each amorphous material layer to have athickness within the prescribed thickness while sandwiching othermaterial layers between the amorphous material layers, the process ofcrystallizing the amorphous material can be reduced to only one at thetime of ending the whole process.

However, in general, the stress generated is lower when crystallizationand shrinkage is carried out in the state when the surface boundarycondition of the amorphous material layer is free. Therefore,crystallization may be carried out each time after the completion ofdepositing a film of each divided amorphous material layer. It is alsogood to carry out an irradiation of a laser beam to a local portion ofthe divided amorphous material layer, selectively apply a low stress tothe local portion and crystallize the portions, not directly related toa failure, at the time of the completion of the whole process.

By using the above-described method of manufacturing a semiconductordevice, it is possible to manufacture a gate electrode without causing astress generated within the film of the gate electrode to exceed acritical stress level corresponding to a fail event and with a targetfilm thickness and with a low resistance of a uniform and high impuritydensity, in the same manner as in the first embodiment. Thus, a highlyreliable product can be provided.

Although the p-type silicon semiconductor substrate 4 has been used as asemiconductor substrate in the second embodiment, the semiconductorsubstrate need not be the p-type but an n-type silicon semiconductorsubstrate can also be used. A gallium arsenide semiconductor may also beused as an alternative. Although polycrystalline silicon has been usedas the material for the gate electrode 8, other conductive material mayalso be used when this can be deposited in an amorphous state and whenit is crystallized. Although P (phosphorus) has been used as animpurity, other impurity such as B (boron) or As (arsenic) may also beused.

Another embodiment of a semiconductor device structure manufactured byusing the method of manufacturing a semiconductor device based on thepresent invention will be explained with reference to FIGS. 18 to 24.

FIGS. 18 to 24 are cross sections in the embodiment of the semiconductorstructure according to the present invention. The present invention isused to bury a trench (a rugged surface) formed on the surface of thep-type silicon semiconductor substrate 4 with polycrystalline siliconlayers 6.

FIG. 18 shows an example that the present invention is utilized for atrench-type memory cell, according to which a silicon oxide film 5 isformed as an insulation film in a trench on the surface of the p-typesilicon semiconductor substrate 4 and then the polycrystalline siliconlayers 6 are deposited to fill the trench. As shown in FIG. 19, thistrench may not necessarily be completely filled with the polycrystallinesilicon layers 6.

FIG. 20 shows an example that polycrystalline silicon layers 6 aredeposited on the surface of the p-type silicon semiconductor substrate 4of which corner portions have been rounded by an isotropic etching orthe like or the corners have been lost by covering them with aninter-layer insulation film for flattening the corners. FIG. 21 shows anexample that the side surface if trench and step portions is tapered.FIG. 22 shows an example that there is a rugged surface at the sidesurface of trench and step portions. There is no roundness at thecorners and stress is concentrated when the corner is acute, with asevere structure.

FIGS. 23 to 25 show an example that films of polycrystalline siliconlayers 6 have been deposited as wiring layers at steps. Films of thewiring layers 6 are deposited on a rugged surface of the surface of ap-type silicon semiconductor substrate 4 after a gate electrode 2 andothers have been covered with an inter-layer insulation film 16, and thedeposition of the wiring layer films 6 is also used to take an electriccontact with the substrate.

In the case of depositing and crystallizing amorphous silicon, thecorner portion of the step becomes the place where stress isconcentrated along with the volume contraction of the layer due tocrystallization of the amorphous material, so that a large stress isapplied locally as compared with a film formed on a plane portion as inthe case of the first embodiment and the second embodiment.

Accordingly, when the film thickness of amorphous layers such asamorphous silicon to be formed at one time is set so that theconcentrated stress will not exceed a critical stress level and thisfilm forming process is repeated till a necessary film is reached asshown in the first and second embodiments, it is possible to prevent anoccurrence of a failure when films of polycrystalline silicon layers 6are deposited at the step when the polycrystalline silicon layers 6 areburied in the trench formed on the surface of the p-type siliconsemiconductor substrate 4.

The shape of the side wall and corner of the step as shown in FIGS. 23to 25 may be the shape as shown in FIGS. 20 to 22 or a combination ofthese shapes.

When an amorphous material is used to deposit films in a trench and on astep, the effect of the method of manufacturing a semiconductor deviceaccording to the present invention is best exhibited by depositinglayers by setting a film thickness of the amorphous layers deposited atone time to be not larger than a critical stress value.

A similar effect can also be obtained when a structure or amanufacturing method of dividing amorphous layers with other materiallayers is used in the second embodiment.

In the above third embodiment, other material such as a tantalum oxidefilm or the like may also be used for the material of an insulation filmof the trench type memory cell. Although amorphous silicon has been usedfor the material for layer lamination, other amorphous material may alsobe used instead.

A method of manufacturing a thin film according to the present inventionwill be explained with reference to FIGS. 26, 27, 28 and 29. FIG. 26explains a flow of the manufacturing of metal silicide thin filmaccording to the present embodiment. In the present method ofmanufacturing a thin film, a metal silicide thin film of a compositionMSi_(x) (where M is a metal element) is obtained by a chemical reactionofM+xsi=MSi _(x).

After forming a ground film (a silicon oxide film) 5 on a substrate 4, asilicon thin film 6 of a film thickness ½ tSi is deposited. In thiscase, the film thickness tSi is determined by determining a ratio (1:y)of film thickness between a metal thin film 20 and the silicon thin film6 from a density ratio of each element so that the ratio of atomsbecomesM:Si=1:xwhen the composition of the metal silicide film to be finally obtainedis MSi_(x) (where M is a metal element). In other words, the followingrelation is obtained:tM:tSi=1:y   (1)

Consider a ratio (1:z) of a film thickness tMSi which is two times thefilm thickness calculated from the thickness of the metal silicide thinfilm per one layer to be prescribed by a fail event to be obtained inthe end to a film thickness of the sum of the film thickness tSi of thesilicon thin film and the film thickness tM of the metal thin,film, thatistmSi:(tSi+tM)=1:z   (2)

By eliminating tM from the expressions (1) and (2), the followingexpression is obtained:tsi=(yz)tMSi/(1+y)   (3)

Then a metal thin film to be determined by a film thickness shown belowis deposited as the film of the second layertM=ztMSi(1+y)   (4)

For a third layer, a silicon thin film of the film thickness tSi isdeposited. The metal thin film 20 of the film thickness tM and thesilicon thin film 6 of the film thickness tSi are deposited alternatelyby a necessary number of layers (N layers). The number of layers(considering a pair of the metal thin film and the silicon thin film asone layer) necessary for depositing becomes an integer which satisfiesN=TM/tMSiwhen the film thickness of the metal silicide thin film to be obtainedin the end is tM. However, tMSi is adjusted so that N becomes an integerat a film thickness not higher than the critical film thickness to beprescribed by a fail event.

The film thickness of the top layer is set to be ½ tSi or ½ tM. Thereason for the film thickness of the bottom layer and the top layerbecoming ½ is as follows. Since a chemical reaction starts from theinterface of different kinds of materials, the chemical reactionprogresses from both sides of the upper interface and the lowerinterface for both the silicon thin film 6 and the metal thin film 20.

Accordingly, about the half film thickness of each film is consumed by areaction from the upper interface and the lower interface. In otherwords, only one side of a reaction interface exists in the top layerfilm or the bottom layer film so that the necessary film thicknessbecomes ½.

Although the material of the top layer is a silicon thin film which isthe same as the bottom layer according to the present embodiment, thisneed not be a silicon thin film but a metal thin film may also be good.Further, the film of the bottom layer need not be a silicon thin filmbut the depositing may be started from a metal thin film. Further, themethod of depositing each film is not particularly limited.

After completing the depositing of a predetermined number of layers, thewhole substrate is heated to a temperature sufficient enough to progressthe silicide reaction and then the silicide reaction is completed. Anexample of the observation of the crystal state of the film aftercompleting the reaction is shown in FIG. 27. FIG. 27 is an example ofthe observation, by using a transmission electron microscope, of thecrystal structure of a film of laminated layers after a thermalannealing of the film at a temperature not lower than the temperature atwhich a silicide reaction is completed (for example 700° C.) by using acobalt (Co) thin film as the metal thin film and setting the ratio ofthe atomic weight as Co:Si=2:1. A layer i shows a bonding agent for asample of the transmission electron microscope, a layer ii shows acobalt silicon alloy laminated film (Co₂Si) made of about 10 layers inthe picture of FIG. 27, a layer iii shows a silicon oxide film and alayer iv shows a silicon substrate. The layer ii shows a state ofdivided lamination but this is only a color tone difference for eachcrystal because of difference in crystal orientation.

In a state after the completion of the reaction, it is clear that filmshave been formed in a laminated structure in a thickness direction ofwhich layer crystal grains linked in horizontal direction pierce in afilm thickness direction. The thickness of each film corresponds to asilicide film thickness which is determined by ½ of the sum of the filmthickness of the metal thin films and silicon thin films that werelaminated before the reaction, that is:tMSi=½(tM+tSi)/z

As described above, when a silicide reaction is carried out afterlaminating metal thin films and silicon thin films in a plurality oflayers, it is possible to obtain a silicide thin film of a predeterminedfilm thickness in a small crystal grain size, that is, in a low stressstate in which a fail event does not occur, or stress due to a change involume during progressing of a silicide reaction.

FIG. 28 shows a cross section of a MOS (metal-oxide-semiconductor)transistor manufactured by applying the present manufacturing method,which shows a state that a silicide alloy has been used for a gateelectrode of the transistor.

According to the present embodiment, a gate electrode of a predeterminedfilm thickness is formed by a laminated film made of small crystalgrains so that the stress at the time of manufacturing a silicide filmcan be controlled to be not higher than the stress at the time of anoccurrence of a fail event.

FIG. 29 shows a cross section of a semiconductor device that has beenmanufactured by using silicide thin films 19 as a wiring materialaccording to the present manufacturing method. In the presentembodiment, it is also possible to structure a wiring film of apredetermined film thickness by a laminated film of small crystal grainsso that the wiring film can be manufactured in the state of a smallstress in which a fail event does not occur.

As a metal suitable for forming a metal silicide thin film, one of thefollowing can be selected: titanium Ti, vanadium V, chromium Cr,manganese Mn, iron Fe, cobalt Co, nickel Ni, tantalum Ta, tungsten W,zirconium Zr, niobium Nb, molybdenum Mo, palladium Pd, rhodium Rh,iridium Ir, platinum Pt, hafnium Hf, terbium Tb, erbium Er and yttriumY.

Thin films in the present invention are to be applied for an opticaldevice, an optical disk, a magnetic disk, interconnection in asuperconductive device, etc.

One embodiment of the manufacturing device according to the presentinvention will be explained with reference to FIGS. 30, 31, 32, 33 and34.

FIGS. 30 and 31 show one embodiment of the manufacturing device using achemical vapor deposition based on the present invention. FIG. 30 showsan example of a diffusion furnace type manufacturing device and FIG. 31shows an example of a vertical manufacturing device.

The manufacturing device according to the present invention ischaracterized in a control unit for automatically controlling arepetitive process of a combination of a plurality of processesincluding a process of depositing a film of an amorphous thin film and aprocess of crystallizing this thin film, and the manufacturing devicemay also be a lateral type or others.

The manufacturing devices shown in FIGS. 30 and 31 are structured by achamber 31 for providing a place for a film forming process and aprocess for crystallizing amorphous materials on a semiconductorsubstrate 38, a tool 32 for supporting the semiconductor substrate 38, aheating unit 33 for adjusting the temperature of the semiconductorsubstrate and the atmosphere inside the chamber 31, a plurality of gascontrollers 34 for supplying raw material gases, an exhausting unit 35for controlling the pressure inside the chamber and exhausting airinside the chamber, and an automatic control unit 36 for automaticallycontrolling the manufacturing method based on the present embodimentwith a single unit for manufacturing the semiconductor device.

The automatic control unit 36 controls the heating unit 33, theplurality of gas controllers 34, the exhausting unit 35 and film formingconditions such as the temperature of the semiconductor substrate andthe pressure inside the chamber. A laser irradiation unit 37 as shown inFIG. 31 may also be installed to selectively apply a laser beam to thewhole or a part of the semiconductor substrate 38.

FIG. 32 shows one example of a flow chart of the operation of theautomatic control unit 36 in the unit for manufacturing a semiconductordevice shown in FIGS. 30 and 31. This flow chart is for the automaticcontrol of the processes of the first embodiment shown in FIG. 14. FIG.33 shows one example of the temperature process for automaticallycontrolling the temperature of the semiconductor substrate and thetemperature of the atmosphere inside the chamber as the conditions forforming films, based on the flow chart shown in FIG. 32. In FIG. 33, thehorizontal axis shows time and the vertical axis shows the temperatureof the semiconductor substrate, and T_(cr) shows a critical temperatureat which the amorphous material to be deposited on the semiconductorsubstrate 38 is crystallized.

The flow chart of FIG. 32 will be explained below. In FIG. 32, □ shows aprocessing and ⋄ shows a decision. Assume that the temperature at thetime of starting the process is 20° C., for example. The control of thismanufacturing process of the semiconductor device starts from (100) ofFIG. 32. In processing (101), the semiconductor substrate 38, on whichan insulation film such as a silicon oxide film or the like has beenformed by the sixth process shown in FIG. 7, is installed within thechamber, which corresponds to A in FIG. 33. When inside the chamber hasnot yet reached a vacuum level which is suitable for the environment ofdepositing a film, air is exhausted by using a vacuum exhausting unit.In processing (102), the semiconductor substrate 38 is heated by usingthe heating unit 33 shown in FIG. 30 or FIG. 31. In decision (103), adecision is made whether the temperature of the semiconductor substratehas reached a temperature suitable for depositing an amorphous film. Ifthe temperature suitable for depositing a film has not yet reached, orif a decision of No has been made in the decision (103), the processreturns to the processing (102) and the heating of the semiconductorsubstrate is continued. The loop of the processing (102) and thedecision (103) is repeated until the temperature of the semiconductorsubstrate reaches the temperature suitable for depositing the amorphousmaterial film, that is, until a decision of Yes is made in the decision(103), which corresponds to the processes A to B in FIG. 33. If thedecision (103) is controlled by the heating time, the heating iscontinued until a predetermined heating time has been reached.

After a decision of Yes has been made in the decision (103), processing(104) is carried out by maintaining the temperature suitable fordepositing a film. In the processing (104), a supply of a raw materialgas from the controller into the chamber and the control of the pressureof the raw material gas in the chamber are carried out. In thisprocessing, a film formation of a first divided amorphous material layeris carried out by the chemical vapor deposition method or the like. Indecision (105), a decision is made whether or not the thickness of afirst divided amorphous material layer which is depositing in a film atone time has reached a predetermined value not larger than the thicknessto be prescribed by a critical stress value determined according to afail event. If the film thickness has not yet reached the predeterminedvalue, or if a decision of No has been made in the decision (105), theprocessing returns to the processing (104), and the supply of the rawmaterial gas into the chamber and the control of the pressure of the rawmaterial gas in the chamber are continued. The loop of the processing(104) and the decision (105) is repeated until the thickness of thefirst divided amorphous material layer reaches the predeterminedthickness, or until a decision of Yes has been made in the decision(105), which corresponds to the processes of B to C in FIG. 33. However,if the decision (105) is controlled by a film forming time, theprocessing ( 104) is continued until a predetermined film depositingtime has been reached.

When the thickness of the film deposited has reached a predeterminedvalue not larger than a predetermined thickness to be prescribed by acritical stress value determined according to a fail event, a decisionof Yes is made in the decision (105), and the supply of the raw materialgas is stopped. Then the processing moves to processing (106). In theprocessing (106), the heating unit 33 shown in FIG. 30 or FIG. 31continues to heat the semiconductor substrate 38 until the temperaturereaches a level at which the amorphous material is crystallized. Indecision (107), a decision is made whether or not the temperature of thesemiconductor substrate has reached a temperature at which the amorphousmaterial is crystallized. Similar to the loop of the processing (102)and the decision (103), the loop of the processing (106) and thedecision (107) is also repeated until a decision of Yes has been made inthe decision (107), which corresponds to the processes C to D in FIG.33. However, if the decision (107) is controlled by the heating time,the heating is continued until a predetermined heating time has beenreached.

At the time when the temperature of the semiconductor substrate hasreached a temperature at which the amorphous material is crystallized,the next processing is started. In processing (108), the temperature ismaintained at least for a period of time which is required tocrystallize the whole of the first divided amorphous material layer,which corresponds to the processes D to E in FIG. 33.

After ending the processing (108), a decision is made in decision (109)whether or not the whole thickness of the crystallized layer of theamorphous material has reached a required design thickness. If thedecision (109) is controlled by the number of depositing films of theamorphous material layers, a decision of Yes is made until apredetermined number has been reached. A decision of No is made when thepredetermined number has been reached.

If the thickness of the total layers after the amorphous material hasbeen crystallized does not reach the required design thickness, the filmforming process by using the amorphous material and the crystallizationprocess are repeated again, in a loop of processing (110) and decision(111) so that the semiconductor substrate is cooled until a temperatureis reached at which the amorphous material can be formed in a film,which corresponds to the processes from E to F in FIG. 33.

At the time when the temperature of the semiconductor substrate hasreached a level at which the amorphous material can be deposited in afilm, the processing changes from the decision (111) to the processing(104). In the loop of the processing (104) and the decision (105), theraw material gas is supplied to the chamber and the pressure of the rawmaterial gas inside the chamber is controlled while maintaining thetemperature of the semiconductor substrate 38 at the above temperaturelevel. Thus, a film deposited of a second divided amorphous materiallayer is started. Thereafter, the processings and the decisions from(104) to (111) are repeated until the film thickness of the totaldivided amorphous material layers has reached a required designthickness. If a decision of No has been made in the decision (109) inthe repetition-of the processings and the decisions (104) to (111), orwhen the thickness of the total layers of the crystallized amorphousmaterial has reached a required design thickness, a loop of processing(112) and decision (113), which corresponds to Y to Z in FIG. 33, isstarted. In processing (112), the semiconductor substrate 38 is cooledat a cooling speed which does not cause a failure, due to a thermalstress or the like, in the semiconductor device in manufacturing. In thedecision (113), a decision is made whether or not the temperature of thesemiconductor substrate has reached a temperature for taking out thesubstrate, for example 20° C. temperature of the semiconductorsubstrate.

At the time when a decision has been made in the decision (113) that thetemperature of the semiconductor substrate has reached a level fortaking out the substrate, the processing changes to processing (114) andthe semiconductor substrate 38 is taken out from the chamber of themanufacturing device. By finishing this process of taking out thesubstrate, all the processes controlled by the automatic control unit 36using the manufacturing device based on the present embodiment iscompleted, which corresponds to Z in FIG. 33.

It is needless to mention that the temperature for starting theprocesses and the temperature for taking out the substrate does not needto be 20° C. and the temperature may be any desired level not higherthan the crystallization temperature. Further, the temperature may alsobe not lower than the crystallization temperature, but in this case, theprocessing (102) in FIG. 32 is not heating the semiconductor substratebut cooling the semiconductor substrate and the processing (112) in FIG.32 is heating the semiconductor substrate.

FIG. 34 shows another example of a flow chart of the operation of theautomatic control unit 36 in the unit for manufacturing a semiconductordevice shown in FIGS. 30 and 31. This flow chart is for the automaticcontrol of the processes of the second embodiment shown in FIG. 17. Theflow chart of FIG. 34 is the flow chart of FIG. 32 combined with aprocess of forming a film of other material layers for dividing theamorphous material layers.

Description will be made according to the flow chart of FIG. 34.Processing of □ displayed in a dotted line in the drawing is a processwhich is not necessarily carried out but is carried out when necessary,of which details will be explained later. Assume that the temperaturefor starting the processes is 20° C., for example. The control of themanufacturing process of the semiconductor device is started from (200)in FIG. 34.

Processings and decisions (201) to (205) are the same as the processingsand decisions (101) to (105) in FIG. 32. These processes cover theprocesses up to the process of depositing a film of an amorphousmaterial α. The next process (206) may or may not be carried out at thisstage. In decision (207), a decision is made whether or not a total filmthickness of a layer which has been obtained by crystallizing theamorphous material α and a layer of a material β which is different fromα is smaller than a design film thickness. If there is a layer in whichthe amorphous material α has not yet been crystallized, a decision ismade whether or not the total film thickness of the α and β layers issmaller than a design film thickness when the layer has beencrystallized.

In next processing (208), the temperature of the semiconductor substrateis set under a condition that the material β can be deposited in a film,and by maintaining this environment, the raw material gas of thematerial β is supplied to deposit a film of the β layer. In depositing afilm of the β layer, a raw material gas is supplied as described abovewhen the chemical vapor deposition method or the like is utilized toform the film. However, when a film is to be deposited by the sputteringmethod or the like, instead of the material gas, a gas for colliding anion against a target by accelerating the ion, such as an argon gas, issupplied. The β layer may be deposited in a film in an amorphous stateor in a crystal state. In decision (209), a decision is made whether theβ layer has reached a thickness to be deposited in a film in one time ornot. The loop of the processing (208) and the decision (209) is repeateduntil this film thickness is reached. Next processing (210) may or maynot be carried out at this stage.

In processing (211), similar to the decision (207), a decision is madewhether or not a total film thickness of a layer which has been obtainedby crystallizing the amorphous material α and a layer of a material βwhich is different from α is smaller than a design film thickness. Ifthere is a layer in which the amorphous material α has not yet beencrystallized, a decision is made whether or not the total film thicknessof the α and β layers is smaller than a design film thickness when thelayer has been crystallized.

In the decision (211), if a decision of No has been made, or if adecision has been made that the total film thickness of the α and βlayers has reached a design value, and if all the crystallization of theamorphous material has been finished, the processing proceeds to nextprocessing (212). When a decision of No has been made in the decision(211) and if there is still a layer which has not yet been crystallized,crystallization of the layer which has not yet been crystallized iscarried out before going to the next processing (212). In other words,the processing (206) and the processing (210) do not need to be carriedout each time since the layer of the amorphous material a is depositedby dividing the other material β layer. However, in order to proceed tothe processing (212) by crystallizing all the amorphous material, theremust be provided a process for crystallizing at least one time at any ofthe time of the last processing (206) before moving to the processing(212), the time of the last processing (210) before moving to theprocessing (212) or immediately before the processing (212).

The above-described process of crystallizing the amorphous material maybe carried out each time after the film formation process of eachdivided amorphous material layer, or the divided amorphous materiallayer may be locally crystallized by a laser irradiation, or thecrystallization may be carried out after finishing the whole filmforming process due to a reason of shortening of the manufacturingprocess, as shown in the second embodiment.

The subsequent processes of the processing (212), processing (213) andprocessing (214) are the same as the processes of the processing (112),the processing (113) and the processing (114). In other words, thesemiconductor substrate is cooled until the temperature has reached alevel for taking out the substrate, for example 20° C., and thesemiconductor substrate is taken out from the chamber of themanufacturing device, so that the whole processes controlled by theautomatic control unit 36 which uses the manufacturing device based onthe present embodiment is finished.

It is needless to mention that the temperature for starting theprocesses and the temperature for taking out the substrate does not needto be 20° C. and the temperature may be any desired level not higherthan the crystallization temperature. Further, the temperature may alsobe not lower than the crystallization temperature, but in this case, theprocessing (202) in FIG. 34 is not heating the semiconductor substratebut cooling the semiconductor substrate and the processing (212) in FIG.34 is heating the semiconductor substrate.

As described above, when the unit for manufacturing a semiconductordevice is utilized, it is possible to manufacture a semiconductor devicehaving a low stress structure, explained in the first embodiment, thesecond embodiment and the third embodiment, in the same chamber in aconsistent process by an automatic control. Therefore, a semiconductordevice in manufacturing can be effectively controlled without exposingthe semiconductor device to the atmosphere.

Next, an embodiment relating to the manufacturing device of the presentinvention will be explained with reference to FIGS. 35 and 36. FIG. 35is a cross sectional configuration diagram of a bipolar sputtering unitwhen the sputtering method is employed as a method of forming a thinfilm. A material target 41 for forming a film and a substrate 38 fordepositing a film face each other, and a DC or AC voltage is appliedbetween the target 41 and the substrate 38 from a power source 39 and adischarging gas, for example an Ar gas, introduced through a gascontroller 34 is discharged.

The substrate 38 is held by a holder 32 having a heating function andthe temperature of the holder 32 is controlled by a temperaturecontroller 40. A speed of depositing a thin film is adjusted bycontrolling the pressure of an introduced gas, an applied voltage or thetemperature of the substrate by a control unit 36. The temperatures ofthe substrate 38 and the holder 32 are also controlled by the controlunit 36.

The method of controlling the speed for depositing a thin film and thetemperature of the substrate will be explained with reference to FIG.36. FIG. 36 shows an example of time controlling a speed V fordepositing a thin film and a temperature Ts of the substrate. At thetime of starting the depositing of a thin film, the temperature of thesubstrate is held at a sufficiently lower level than the temperature ofcrystallization.

In this state of the temperature, a first layer film is deposited withina predetermined film thickness range prescribed by a fail event (L1).Then, the depositing of a thin film is stopped and a crystallizationreaction of a film that has been deposited by increasing the substratetemperature Ts to a crystallization temperature Tc or above is completed(C1). The temperature control is carried out so that the crystallizationis within the range of the primary recrystallization reaction, that is,the crystallization is carried out so that a film thickness is obtainedby a 5 deposition of grown grains of average grain size.

After completing the crystallization reaction, the substrate temperatureTs is lowered to be not higher than the crystallization temperature Tcand the film deposition is started again. When the thickness of thedeposited films has reached a predetermined thickness, the deposition offilms is stopped and the substrate temperature Ts is increased tocrystallize a second layer deposited film (C2). The deposition of thinfilms can be stopped by stopping an application of a discharge voltage,or by dropping the discharge voltage to not higher than a dischargecritical voltage, or by stopping an introduction of a discharge gas orby controlling a gas pressure to outside the discharging area. Theheating of the substrate can be achieved by keeping a heater or the likein the holder 32.

It is needless to mention that although films are deposited two times inthe present embodiment, that is L1 and L2, the number of depositingfilms is not limited to two times but the film deposition may be carriedout by a required number of times.

According to the present embodiment, in a manufacturing device fordepositing thin films of a predetermined film thickness, it is possibleto provide the unit which can continuously carry out depositing of filmsby a plurality of times of which film thickness is not larger than amaximum film thickness to be prescribed by a fail event andcrystallization of each deposited film, without taking out the substratefrom the unit. Therefore, there is an effect that it is possible toprovide a manufacturing device which can deposit thin films of apredetermined film thickness of a low stress without an occurrence of afail event.

Another embodiment of the method of manufacturing thin films of thepresent invention will be explained with reference to FIGS. 37, 38, 39and 40. FIG. 37 shows a method of manufacturing a laminated thin filmstructure unit according to the present embodiment.

On the surface of a silicon substrate 4, a base film, that is a siliconoxide film, is formed, and amorphous thin films into which an impurityof a predetermined density has been doped, such as for example amorphoussilicon thin films, are deposited within a range of a film thicknesswhich does not cause an occurrence of fail event, and then thecrystallization reaction of the deposited thin films is completed.

Into a second layer amorphous silicon thin film, an impurity is dopedhaving a density higher than the density of the first layer and then thecrystallization reaction of the film is completed. The density of athird layer film is set to be the same as the density of the secondlayer film, and an impurity of the density same as the density in thefirst layer film is doped in a fourth layer. Then the crystallizationreaction of the respective layers is completed.

According to the present embodiment, a polycrystalline silicon thin filmof a predetermined film thickness can be obtained as a laminated thinfilm structure of small grain size, so that the film can be deposited ina low stress state and a gradient of an impurity density can bedeposited in a film thickness direction. The number of the film layersto be laminated does not need to be four as described in the presentembodiment.

It is also needless to mention that the profile of the impurities to bedoped in the layers does not need to be the profile as shown in FIG. 38but any desired profile can be formed to meet an object.

FIG. 39 is a cross section of a MOS transistor that has beenmanufactured by applying the method of manufacturing a thin filmaccording to the present embodiment. It is also good to consider a caseof using P as an impurity to reduce an electric resistance. In thiscase, the density of P in the first layer is controlled to be low asshown in FIG. 38 in order to minimize an occurrence of a deteriorationof an oxide film due to a diffusion of P in the oxide film.

According to the present embodiment, there is an effect that a lowstress can be obtained by having a polycrystalline silicon thin film,which becomes a gate electrode, as a laminated film structure of whichcrystal grain size is small. Also, there is an effect that the profileof an impurity density in a film thickness direction can be controlledto meet an object. It is needless to mention that the number ofdeposited layers for the gate electrode film is not limited to four asshown in the present embodiment. The profile impurity may also bedifferent from the one shown in FIG. 38.

FIG. 40 shows an example of the cross section of a wiring thin filmstructure for a semiconductor device for which the method ofmanufacturing a thin film according to the present embodiment has beenapplied for the manufacture of the wiring film. Consider a profile ofimpurity as shown in FIG. 38, for example. Electric resistance of secondand third layers whose impurity density is high is lower than theelectric resistance of first and fourth layers so that a currentselectively flows through the second and third layers.

In this case, Joule heat is generated mainly in these two layers so thatthe temperature of the first and fourth layers becomes relatively lowand surface diffusion of atoms ruling the electromigration isrestricted, with a result that electromigration-proof life may beimproved.

In the present embodiment, the number of deposited layers of films inthe film thickness direction is not limited to four and the profile ofimpurity density may also be different from the one shown in FIG. 38. Inthe present embodiment, a thin film whose profile of impurity density inthe film thickness direction has been controlled to meet a predeterminedobject can be obtained as a laminated film structure of fine grain size.Therefore, there is an effect that a thin film structure can be providedin a low stress state which does not cause an occurrence of a failevent.

An embodiment of a method of determining a film thickness according tothe present invention will be explained with reference to FIGS. 41, 42and 43. FIG. 41 shows a flow chart of the method of determining a filmthickness according to the present invention. An initial value of a filmdivided number N is set as 1.

A critical stress exists in each of a mechanical fail event caused by astress of a film, such as a peeling off or crack of a film, or in anoccurrence of a dislocation in a monocrystalline substrate. Thus, inprocessing (300), a critical stress σ_(c) corresponding to a mechanicalfail event which occurs in an object process is determined. Inprocessing (301), a necessary total film thickness T_(t) is determinedbased on a cross sectional area of a wiring or the like which satisfiesa necessary design resistance value or based on a surface area or thelike which satisfies a capacitance value or the like.

In a crystallization reaction or a silicide reaction, there is acorrelation between a crystal grain size L_(c) after the completion of areaction and a stress σ generated by a film, as shown in FIG. 42. Afunction which shows the relation between the two is the function of acrystal grain size before or after the reaction and Young's modulus ofthe film, etc. In process (302), the relationship between the grain sizeand the film stress, that is, σ=f (L) is obtained. Since a criticalstress σ_(c) exists in each of a mechanical fail event caused by astress of a film, such as a peeling off or crack of a film, or in anoccurrence of a dislocation in a monocrystalline substrate, the criticalcrystal grain size L_(c) is determined according to each fail event.

In general, it has been known that when a primary recrystallizationreaction has been generated in a thin film by thermal annealing, acrystal grain size becomes about a film thickness as a result.Accordingly, considering this primary recrystallization reaction, arelationship between the film thickness and the generated stress can beknown as shown in FIG. 43. In processing (303), the relationship betweenthe film thickness and the generated stress, that is σ=g(T) is obtained.It is also possible to obtain a critical film thickness T_(c)corresponding to the critical stress σ_(c) of a mechanical fail eventaccording to each fail event in a similar manner. Once a film thicknessT_(u) per one layer to be deposited has been determined, a stress σ_(u)generated in the film per one layer, when a crystallization reaction ora silicide reaction has been generated one time to an amorphous materiallayer of the determined film thickness, can be readily read from FIG.43. Therefore, it is possible to decide whether the generated stressσ_(u) can cause a fail event to occur or not.

In decision (304), a decision is made whether the stress generatedinside the film is not larger than the critical stress σ_(c) or not. Ifthe generated stress is hot larger than the critical stress value of afail event, that is, when a decision of Yes has been made in thedecision (304), the film is deposited one time and the crystallizationreaction is completed. In this case, the film thickness in one-time filmformation, which is finally determined in processing (305), becomesT_(u)=T_(t). However, if the generated stress is larger than thecritical stress value at the time of an occurrence of a fail event, orwhen a decision of No has been made in the decision (304), a division ofthe film must be considered.

When a decision of No has been made in the decision (304), theprocessing proceeds to processing (306) and the number of times todivide a film is set as N=N+1. In processing (307), the number ofdivisions of a film N newly determined in the processing (306) is usedto determine a film thickness T_(u) per one layer to be T_(u)=T_(t)/N.In processing (308), the stress σ_(u) generated within the film, whenthe amorphous material layer of the film thickness T_(u) newlydetermined in the processing (307) has been crystallized, is obtainedfrom the relationship between the film thickness and the generatedstress, σ=g(T), that has been obtained in the processing (303).

In processing (309), a decision is made whether a presence or an absenceof an occurrence of a mechanical fail event is to be determined by afinal remaining stress of the film. If a presence or an absence of anoccurrence of a mechanical fail event is to be determined by a finalremaining stress of the film, or when a decision of Yes is made in theprocessing (309), a stress generated in the film is set as Nσ_(u) inprocessing (311), and the loop of the decisions and processings (304) to(309) and (311) is repeated. A division is repeated until a condition,that is, a number of divisions, is obtained under which a sum Nσ_(u) ofthe stress generated within the film that has been divided into N layersdoes not exceed the critical stress value σ_(c) of a fail event. If apresence or an absence of an occurrence of a fail event is notdetermined by the remaining stress of the film but a presence or anabsence of an occurrence of a fail event is determined by a variation ofthe stress per one crystallization reaction or one silicide reaction, orwhen a decision of No is made in the processing (309), a stressgenerated in the film is set as Nou in processing (310), and the loop ofthe decisions and processings (304) to (310) is repeated, and acondition, or a number of division, is obtained under which the stressσ_(u) generated per one film thickness of the film that has been dividedinto N layers does not exceed the critical stress value σ_(c) of a failevent.

The loop of the decisions and processings (304) to (309) and (311) orthe loop of the decisions and processings (304) to (310) finishes at thetime when a decision that the stress generated in the film is smallerthan σ_(c) has been made in the decision (304). Then, in the processing(305), a decision is made of the final film thickness T_(u) per onelayer. In this case, T_(u) which has been determined in the lastprocessing (307) is applied as it is for this T_(u).

In either case, the film thickness of each of the divided film layersdoes not need to be constant but may be different. It is possible todetermine an optimum film thickness of the film to be deposited at onetime in the above-described method. Although not shown in FIG. 41, if afinite division number N can not be obtained or if the division numberis not practical although a finite division number has been obtained,for example when N=10 or above, it is necessary to review the necessarynumber of film thickness T_(t).

According to the present embodiment, there is an effect that it ispossible to easily determine a film thickness to be deposited at onetime when a thin film of a predetermined film thickness is deposited asa plurality of layers to obtain a laminated structure in a low stressstate which does not cause an occurrence of a fail event.

As explained above, when the method of manufacturing a semiconductordevice based on the present invention is used, the thickness of anamorphous layer to be deposited at one time is set to be not larger thana thickness to be prescribed by a critical stress value determinedaccording to a fail event and the film is primary recrystallized so thatit is possible to reduce a stress generated within the polycrystallinelayer due to the crystallization. In the above embodiment, range of theoptimum grain size is 10 nm to 5 μm, and range of the optimum filmthickness is 10 nm to 1 μm.

Further, when thin films with reduced stress are piled to have a crosssectional area that does not cause an excess electric resistance, it ispossible to finally obtain a semiconductor device which can prevent afailure due to a stress and which can prevent a deterioration ofelectric characteristics, an inter-layer peeling off or a crack withinthe layer, with a high reliability and in a high production yield.

Further, when the thin film manufacturing process according to thepresent invention is used, it is possible to control the whole processesof manufacturing a thin film by an automatic control unit which controlsthe process of depositing amorphous layers and the process ofcrystallizing the amorphous material, so that the thin film can bemanufactured by an integrated process without exposing the thin film inmanufacturing to the atmosphere.

Further, by using a method of the present invention for obtaining athickness of an amorphous layer deposited at one time to be determinedaccording to a fail event, it is possible to determine a film thicknessof an amorphous layer that can be deposited at one time to obtain theabove-described effect, which can securely prevent an occurrence of afail event, instead of obtaining a film thickness of the amorphous layerbased on experience.

1. A method of manufacturing a gate electrode, comprising the steps of: forming first amorphous silicon on a gate insulating film; crystallizing said first amorphous silicon to form a first polycrystalline silicon; forming a second amorphous silicon on said first polycrystalline silicon; and crystallizing said second amorphous silicon to form a second polycrystalline silicon.
 2. A method of manufacturing a gate electrode according to claim 1, wherein said gate insulating film is silicon oxide film.
 3. A method of manufacturing a gate electrode according to claim 1, wherein thickness of said first polycrystalline silicon and said second polycrystalline silicon are at most 100 nm.
 4. A method of manufacturing a gate electrode according to claim 1, wherein thickness of said first amorphous silicon and said second amorphous silicon are at most 100 nm.
 5. A method of manufacturing a gate electrode according to claim 1, wherein thickness of said first polycrystalline silicon and said second polycrystalline silicon are sufficiently small such that a fail event in the gate electrode is prevented.
 6. A method of manufacturing a gate electrode, comprising the steps of: forming first amorphous silicon on an oxide film; crystallizing said first amorphous silicon to form a first polycrystalline silicon; forming a second amorphous silicon on said first polycrystalline silicon; and crystallizing said second amorphous silicon to form a second polycrystalline silicon.
 7. A method of manufacturing a gate electrode according to claim 6, wherein said oxide film is silicon oxide film.
 8. A method of manufacturing a gate electrode according to claim 6, wherein thickness of said first polycrystalline silicon and said second polycrystalline silicon are at most 100 nm.
 9. A method of manufacturing a gate electrode according to claim 6, wherein thickness of said first amorphous silicon and said second amorphous silicon are at most 100 nm. 